The origin of the polydispersity in sedimentation patterns of rapidly labelled nuclear ribonucleic acid

Abstract

1. A study was made of the sedimentation properties of purified preparations of the rapidly labelled RNA in the nucleus and the cytoplasm of the HeLa cell. The sedimentation of the rapidly labelled nuclear RNA was very sensitive to changes in ionic strength and bivalent cation concentration. Under the conditions usually used in sucrose-density-gradient centrifugation the rapidly labelled nuclear RNA showed extreme polydispersity, and much of it sedimented more rapidly than the 28s RNA. At low ionic strength and after removal of Mg(2+), however, the rapidly labelled nuclear RNA sedimented as a single peak at about 16s. The conversion of the polydisperse material into the 16s form did not involve degradation of the RNA, since the effect could be reversed by increasing the ionic strength of the solution. 2. The cytoplasm did not contain any RNA that showed polydisperse sedimentation under the usual conditions of sucrose-density-gradient centrifugation, or that had the same sensitivity as the rapidly labelled nuclear RNA to changes in ionic strength. All the radioactivity in the cytoplasmic RNA sedimented with the 28s, 16s and 4s components over a wide range of physical conditions, but these components did contain a labelled fraction with some of the features of the rapidly labelled nuclear RNA on columns of methylated albumin on kieselguhr. 3. In both nucleus and cytoplasm the RNA detected by ultraviolet absorption could also be converted into a 16s form by removal of bivalent cations at low ionic strength; this effect was again, within certain limits, reversible. The nuclear RNA as a whole was more susceptible to changes in ionic strength than the cytoplasmic RNA. 4. It thus appears that all the RNA in the cell, except the 4s RNA, can be prepared, without degradation, as a single peak sedimenting at about 16s. The relationship of these various 16s components to each other is discussed.

The Chain Termini and Alkali-Stable Dinucleotide Sequences in Rapidly Labeled Ribonucleates from L Cells*

“…Thus, it would be advisable to obtain further independent evidence bearing on the polynucleotide chain lengths for the different preparations, particularly for the shorter pulse times. Bramwell and Harris (1967) have suggested that the mean polynucleotide lengths in rapidly labeled RNA preparations may be similar to those for rRNA, and this would be consonant with the present findings. It should be noted that the present estimates, being number-average values, could be different from weight-average estimates for these same preparations, and this will be an important consideration with rapidly labeled RNA specimens, just as it appears that it may be with rRNA specimens (Lane and Tamaoki, 1967).…”

Membrane fluidity, cholesterol and allosteric transitions of membrane‐bound Mg2+‐ATPase, (Na+ + K+)‐ATPase and acetylcholinesterase from rat erythrocytes

“…58 mCi/mmole) was purchased from New England Nuclear and diluted with cold steroid as indicated in table 3. The final membrane suspension was solubilized in 5 ml of scintillating fluid [6] and counted in a Packard Tri Carb Scintillator Counter.…”

Cell Biology of Acetabularia

“…This is in accordance with results of BALTUS and QUERTIER (1966) but in contrast to what is known of other organisms. Since it seems improbable that the ratio of 1 : 2 in Acetabularia is due to degradation under the conditions used, one has to consider an interconversion of the two components (BRAMWELL and HARRIS, 1967;HAR-RIS, 1968) or a peculiar structure of A cetabularia ribosomes. It proved difficult to avoid degradation of RNA during the preparation of RNA from enucleated Acetabularia (DILLARD and SCHWEIGER, 1969).…”